The invention relates to the field of optical communication, and in particular to integrated optical networks without polarization sensitivities.
The amount of digital data processed around the globe grows rapidly every year. To perform almost any kind of operation on optical signals today (like wavelength conversion, pulse regeneration, bit-rate conversion, logic operation, etc.) the signals first need to be converted to the electronic domain. Unfortunately, there are fundamental physical reasons that prevent electronics from operating well at high frequencies. As a result, the price of electronic components grows rapidly when higher bit-rates are needed. Consequently, using all-optical signal processing becomes rapidly more and more appealing.
Lossless guiding of light at length-scales approaching the wavelength of the light itself is a necessary property for any future integrated optical circuit. Most of the research in the area of all-optical devices today is in high-index-contrast integrated optics. While high index-contrast dielectric waveguides can reduce radiation losses from features such as sharp bends, they cannot completely suppress them and are in general very sensitive to roughness. Furthermore, they are highly polarization sensitive. Given that the polarization-state of an input signal may not be known and/or may vary over time, their proper operation would require the use of active polarization pre-processing devices. Research towards creating polarization-insensitive bends has been successful only at bends with a large radius of curvature, which however, is not useful for optical integration. In general, any feature of the integrated optical network other than a straight segment of a waveguide, will introduce radiation losses and polarization sensitivity, compromising the performance. An ideal system would be the one that suppresses both these mechanisms.
Photonic crystals have been shown in certain cases to eliminate radiation loss and thus offer a promising platform for designing high-performance waveguide networks. A common drawback, however, to all photonic-crystal waveguide systems proposed to-date, is that they are highly polarization selective.